期刊
出版社
INT UNION CRYSTALLOGRAPHY
DOI: 10.1107/S2052520619001963
关键词
zirconium niobate Zr6Nb2O17; zirconium tantalate Zr6Nb2O17; hafnium niobate Hf6Nb2O17; hafnium tantalate Hf6Nb2O17; crystal structure solution; synchrotron X-ray powder diffraction; neutron powder diffraction
资金
- National Science Foundation, Division of Materials Research [1411032]
- US Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-AC02-06CH11357]
- Division Of Materials Research
- Direct For Mathematical & Physical Scien [1411032] Funding Source: National Science Foundation
Zr6Nb2O17, Hf6Nb2O17 and Hf6Nb2O17 crystal structure solutions have been solved using synchrotron X-ray powder diffraction and neutron powder diffraction in conjunction with simulated annealing, charge flipping and Rietveld refinement. These structures have been shown to be isomorphous with the Zr6Nb2O17 superstructure, leading to the classification of the A(6)B(2)O(17) (A = Zr, Hf; B = Nb, Ta) orthorhombic compound family with symmetry Ima2 (No. 46). The asymmetrical structural units of cation-centred oxygen polyhedra used to build the structure are as follows: (i) one set of symmetry-equivalent six-coordinated polyhedra, (ii) three sets of symmetry-equivalent seven-coordinated polyhedra and (iii) one set of symmetry-equivalent eight-coordinated polyhedra. The potential for cation order and disorder was discussed in terms of cation atomic number contrast in X-ray and neutron powder diffraction as well as the bond valence method. In addition, the structural mechanisms for experimentally observed compositional variations within the solid solution range can be attributed to the addition or removal of a set of symmetry-equivalent seven-coordinated polyhedra accompanied by corresponding oxygen tilts within the A(6)B(2)O(17 )structure.
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